package org.bouncycastle.crypto.generators;

import java.math.BigInteger;
import java.security.SecureRandom;

import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator;
import org.bouncycastle.crypto.KeyGenerationParameters;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECKeyGenerationParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.math.ec.ECConstants;
import org.bouncycastle.math.ec.ECPoint;

/**
 * 椭圆曲线密钥对创建器
 * 
 * @author john.peng
 *
 */
public class ECKeyPairGenerator implements AsymmetricCipherKeyPairGenerator, ECConstants {
	ECDomainParameters params;
	SecureRandom random;

	public void init(KeyGenerationParameters param) {
		ECKeyGenerationParameters ecP = (ECKeyGenerationParameters) param;

		this.random = ecP.getRandom();
		this.params = ecP.getDomainParameters();
	}

	/**
	 * Given the domain parameters this routine generates an EC key pair in
	 * accordance with X9.62 section 5.2.1 pages 26, 27.
	 */
	public AsymmetricCipherKeyPair generateKeyPair() {
		BigInteger n = params.getN();
		int nBitLength = n.bitLength();
		BigInteger d;

		do {
			d = new BigInteger(nBitLength, random);
		} while (d.equals(ZERO) || (d.compareTo(n) >= 0));

		ECPoint Q = params.getG().multiply(d);

		return new AsymmetricCipherKeyPair(new ECPublicKeyParameters(Q, params), new ECPrivateKeyParameters(d, params));
	}
}
